Tieline swing relay

ABSTRACT

Power and rate of change of power transmitted in an electrical network are used to detect network instability. A power signal, a rate of power change signal, and a residual flow compensating signal are summed to indicate network condition. When a design maximum is exceeded a trip relay initiates sectionalization of the network. Selective response of the relay, to preclude operation by transients, is provided by limiting the rate signal, and by blocking the summation signal where design incorporated maxima are exceeded.   D R A W I N G

United States Patent Inventors Ferber R. Schleif [56] References CitedDenver, Colo.; UNITED STATES PATENTS A I No gfig' Edgewate" 3,254,2305/1966 Wahrer 328/150 Y 1968 3,379,934 4/1968 Hoe] et al. 317/27 aPatented Jan. 26,1971 3,419,757 12/1968 Steen 317/36(TD) Assignee theUnited States of America as represented m y n -Har ld Bro me by th Se etf th I t i Attorneys- Ernest S. Cohen and Gersten Sadowsky ABSTRACT:Power and rate of change of power transmitted in an electrical networkare used to detect network instability. A power signal, a rate of powerchange signal, and a residual g 'y gg q i f flow compensating signal aresummed to indicate network alms rawmg condition. When a design maximumis exceeded a trip relay U.S. Cl 317/27 initiates sectionalization ofthe network. Selective response of Int. Cl H02h 3/28 the relay, topreclude operation by transients, is provided by Field of Search 317/27,33, limiting the rate signal, and by blocking the summation signal36(TD), 36(D); 328/150; 307/126 where design incorporated maxima areexceeded.

I0 I'- l5 3a\ RESIDUAL FLOW 1 /4 l 22 GOMSPSBSATION I RCE 4o 1 46 I T 2AMPLIFER 24 TRANSDUCER CIRCUIT SUMMER 42 BLOCKING 48 l iY I 50 I 3 0 3NETWORK CIRCUIT T I 26 DIFFERENTRATOR l l CIRCUIT II I l J TIELIN ESWING RELAY BACKGROUND OF THE INVENTION This invention relates toelectrical relays and more particularly. to a relay system which issensitive to the power characteristics of interarea electricaltransmission system ties.

Interconnection of large power systems with long transmission linesrequires close surveillance of the interconnected system to detect theapproach of unsatisfactory performance. Oscillations, excessiveinterchange, inadvertent interchange, or out-of-step conditions harmfulto the power system must be discovered in ample time for correctiveaction to be taken. The relay of the present invention is designed todetect the approach of these harm harmful conditions and bring aboutsectionalization before the conditions exceed tolerable limits in theassociated system.

Prior devices employed in the monitoring and control of power systemshave included relays I sensitive to the impedance, voltage, current orpower of the system to detect harmful conditions. Thesedevices weresensitive only to fault conditions in the system and not 'to thedevelopment of dynamic instability.

The relay of the present invention overcomes the limitations of theprior art by operation in response to functions of tieline power. Alonga single interarea system tie, power variations of an oscillatory natureare mainly confined to a natural frequency which is characteristic ofthat tie and of the inertia of the interconnected system. Powervariations at a much slowerand irregular rate are also present due tothevariation of system loads and the action of area generation control.The tolerable limits of these interchanges are best id'entifiedat thecritical tie, rather than elsewhere in the system. Therefore, tielinepower is employed as the quantity upon which this relay operates.

The relay employs power and rate of change of powerin determining itsoperating point. Thesensitivity of the relay to each of these quantitiesis adjustable to suit desired limits or characteristics of the tie.Either power or rate may be used alone if conditions require, but it ismost advantageous to use the combination for greatest sensitivity in theearly detection of undesirable conditions. t

The relay of the present invention is connected to. a transmissionsystem tieline through a'power transducer. The transducer measures thesystemjpower and provides a voltage-output representative of themagnitude and direction of power transmission in the system. The outputof the transducer is fed to an amplifier, the output of which ischaracteristic of the system power. The amplifier output issimultaneously fed into a differentiating network and into a summer. Thedifferentiating network measures the rate of change of power andprovides a corresponding rate signal which is fed into a limiter. Thelimiter controls'the rate signal and blocks passage of current for highrate changes. The output of the limiter is fed into the summersimultaneously with the power signal from the amplifier. An adjustablebiassignal, for offsetting residual flow characteristics of the systemis also fed into the summer. The

output of the summer, which provides an indication of power developmentin the tieline, is fed to a trip relay through an intermediate blockingnetwork. The blocking network selectively blocks the connection betweenthe summer andtrip relay for signals indicating excessive rates ofchange of system power. An output from the differentiator is fed intothe blocking network, activating the network when excessive rates a ofchange are sensed by the differentiating circuit to prevent activationof the trip relay by spurious transients.

The relay. is bidirectionally sensitive to disturbances in thetransmission system. Since tielines are used to transmit power in eitherdirection as system needs change, provision ismade for powerdisturbances occurring in either direction of transmission to activatethe relay. Overload power alone, independent of the rate of change ofpower, is sufficient to produce relay tripping for power flow in eitherdirection.

Sensitivity to oscillatory conditions and anticipation of pullout in thepresent invention are provided by the rate of change of power feature.Overall selectivity is improved by combining the power and rate ofchange of power features. Thus, if the increase of power is slow andaperiodic, in-. terchange up to the chosen steady limit is tolerated.However, at an appreciably lower value of power interchange, if thepower increases rapidly, the rate-of-change signal in combination withthe power signal produces tripping at a lower level of power inanticipation of the power limit that will be reached. The power and ratesignals are both bipolar and add vectorially. If the power is high butdecreasing, the rate signal subtracts from it and the trip point is mademore remote. Even though the relay may be swinging through zerointerchange, if the swing is great enough tripping may be produced bythe rate of change alone.

Under ideal conditions on a single tie between well-inte'grated areasthe power and rate sensitivity are selected to approximate the stabilitylimits of the tieL Where the interconnected areas themselves have othercritical ties, unsatisfactory conditions such as fluctuating voltageduring oscillations may precede the stability limit. In these instancessensitivity permitting reasonable continuity of the tieline is the mostpractical choice.

Where the tieline from which power for the relay is measured isparalleled by another line or combination of lines, coordination becomesmore difficult as a result of both steady state and transientconditions. The steady state power flow on the metered line is no longernecessarily proportional to the net interchange. There may be a residualflow on the tie when the net interchange is zero. This residual flow mayvary in magnitude and direction as the distribution of generation ischanged on or near the parallel lines. If the residual flow for anydistribution of generation is subtracted from that seen by the relay,the remainder is again reasonably representative of the net tie. Aresidual flow compensator is therefore provided in the relay to subtractout this quantity.

Transient conditions which must be discriminated are greatly complicatedby parallel tieline paths. The increased complication results from theincrease in the rate of change for an oscillation of given amplitude asthe frequency increases. Moreover, the natural frequency for a transientdisturbance on one of the parallel or adjacent line sections is normallyhigher than that for the net interarea tie. Hence, without specialprecautions these minor local disturbances can produce higherrate-of-changesignals than the net tie. Special precautions employed toprevent tripping from these undesirable causes include limiting of therate signal, filtering,

' and selective blocking.

It is therefore an object of the present invention to provide a It is afurther object of this invention to provide a relay sensitive to the therate of change of power transmission in an electrical system.

It is a further object of this invention to provide a relay sensitive tothe combined effects of power and the rate of change of powertransmission in an electrical system.

It is a still further object of this invention to provide a powersensitive relay in which residual power flow effects are It is a stillfurther object of the present invention to provide a relay which isselectively sensitive to power and rate of change of power transmissionin an electrical system, incorporating limiting and blocking functionsto preclude relay activation by spurious signals.

These and other objects of the present invention will become more fullyapparent with reference to the following BRIEF DESCRIPTION oFr-IIEDRAWING FIG. 1 is a block diagram showingthe tieline'swing relayconnected to a transmission line fragment through an intermediate watttransducer.

FIG. 2 is a schematic representation of the tieline swing relay enclosedby dotted lines in FIG. 1.

FIG. is a schematic representation of a blocking network indicated inblock form in FIGS. land 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The tieline swing relay of thepresent invention is schematically shown in FIG. 1 connected to atransmission line fragment 12 through a power transducer 14. Powertransducer signal, the magnitude and sign of which are representative ofthe power transfer detected by the transducer. The output of amplifiercircuit 22 is fed through lines 24 and 26 respectively, to a summercircuit 28 and a differentiator circuit 30.

Differentiator circuit 30 measures the rate of change of the amplifiedpower signal from amplifier circuit 22 and provides an output signal atline 32 representative of this rate of.

change. The rate signal from the differentiator 30 is fed into a limitercircuit 34 which controlsthe range of the rate signal and compensatesfor high rate changes induced by transients and spurious signals oflittle immediate change to the transmission line 12.

The output of limiter circuit 34 is fed through a line 36 to summercircuit 28 where it is added to the output of amplifier circuit 22 toform a signal representative of the combined amount and rate of changeof power transferred in line 12. The output of a residual flowcompensation source 38 is s similarly fed through a line 40 to summer 28and combined with the amount and rate of change of power signals toforma representative power signal in output line 42 of the summer.

The output of the residual flow compensation source 38 is set at a levelto neutralize the residual power flow on the transmission line 12 whenthe net system interchange of power through the line 12 is zero. Theoutput from the summer in line 42, therefore, represents those powertransfer parameters of line 12 which are significant for protection ofthe line.

The output of summer circuit 28 is fed through a blocking network 44 toa trip relay by intermediate lines 42 and 48. When the combined inputsignals to summercircuit 28 exceed a critical design maximum,characteristic of line 12 and the network it interconnects, the summeroutput signal activates trip relay 46. The outputof trip relay 46 thenactivates conventional circuit interruption equipment (not shown)through an interconnecting line 50.

The relay circuit 10 will now be described in particular detail withreference to FIG. 2. The output of a power (watt) transducer 14, asshown in FIG. 1, is connected to the positive and ground input terminals52 and 54, respectively, of the relay 10. The power transducer providesa DC voltage output, characteristic of power transfer on thetransmission line. The polarity of the power transducer output signal ispositive for one direction of power flow and negative for the otherdirection. The power transducer, itself, is well known and forms no partof the present invention. Terminals 52 and 24 of relay circuit 10connect the power transducer 14 with amplifier circuit 22 of the relay.The amplifier circuit includes filters F 1 and F respectively, in serieswith and parallel to an amplifier 54, which may comprise a vacuum tubeor suitable solid state element. Filters F and F include resistors andcapacitors R R and C and R and C respectively. The filter time anamplifier circuit 22, which provides'an amplified output constants arechosen to eliminate l 20l-lz ripple and signal hash above the relayoperating range. Amplifier 54 is provided with suitable grounding atterminals G and with suitable voltage input from positive terminal 56and negative terminal 58 of a power supply 60. The voltage at terminals56 and 58 is of equal magnitude and opposite sign with respect toground. Since the implementation of suitable amplifiers in the presentinvention will be apparent to those of ordinary skill in the art. theinternal function of the amplifier will b not be described in furtherdetail.

Power supply 60 is connected to a suitable AC source of electrical power(not shown) at grounded input terminal 62. Low voltage AC output isprovided at terminal 64, and'equal DC voltages of opposite sign areprovided at positive terminals 56 and negative terminal 58, as describedabove. A stepdown transformer 66 is connected in parallel with powersupply 60 and provides low voltage AC at transformer output terminals 68and 70.

- The output of amplifier circuit 22 is fed to summer circuit 28, whichserves as the relay driver, via aconductor 24, and to differentiatorcircuit 30 via a conductor 26. Conductor 24 is connected in series witha potentiometer 72, one terminal of which is connected to ground. Thetap of potentiometer 72 is connected to a common input lead 74 of summercircuit 28 through a resistor R Potentiometer 72 facilitates adjustmentof the sensitivity of relay 10 relative to the amount of powertransferred by line 12, enabling selective proportioning-of the amountand rate of change of power signals which are combined to determinerelay tripping.

Differentiator circuit 30 includes'a capacitor C and resistor R inseries with an amplifier 76, and a resistor R and a capacitor C each inparallel with the amplifier. T he operational connections of amplifier76 are similar to those described for amplifier 54, as are those of theother amplifiers in the relay 10, and will not be described in detail.The values chosen for R and C determine the threshold at which blockingnetwork. 44 is activated. Increasing the value of resistor R whilecorrespondingly decreasing the, value of capacitor C to preserve thefilter time constant of the differentiator, increases the sensitivity ofthe blocking function.

The rate representative output of differentiator 30 is fed throughconductor 32 and series-resistor R to an amplifier 78 in limiter circuit34 of the relay. A resistor R potentiometers 80 and 82, and a resistor Rare connected in series between positive and negative terminals 56 and58 of power supply 60. The low voltage terminal of potentiometer 80 andthe high voltage terminal of potentiometer 82 are joined to the outputof amplifier 78 at a terminal 84. A'diode D, is joined between thevoltage tap of potentiometer 80 and the input to amplifier 78 ,with thecathode of the diode joined to the potentiometer tap. Another diode D isjoined between the input of amplifier 78 and the voltage tap ofpotentiometer 82 with the anode of diode D joined to the potentiometertap. A feedback resistor R is joined in parallel between the input andoutput terminals of amplifier 78 to provide amplifier gain feedback.Simultaneous adjustment of potentiometers and 82 is'achieved by linkage86, to provide positive and negative rate sensitivity limits adjustment.The adjustable limiter circuit 34 precludes excessive sensitivity athigher rates of swing than those characteristic of the tieline by addingappropriate positive or negative neutralization voltages through diodesD and D when the magnitude of the rate input to amplifier 78 exceeds apositive or negative design maximum, variable by adjustment ofpotentiometers 80 and 82.

The output of limiter circuit 34 is connected to a terminal of apotentiometer 88, the other terminal of which is connected to ground.The voltage tap of potentiometer 88 is connected to common input lead 74of summer circuit 28 through a seriesresistor R Potentiometer 88facilitates adjustment of the sensitivityofrelay 10 -relative to therate of power transferred by line 12.

Still more ideal combination of the power and rate terms is obtained ifthese terms are squared before combination by substitution of squaringnetworks for resistors R R A potentiometer 90 is joined between positiveand negative terminals 56 and 58 of power supply 60 to provide a voltageoutput for residual flow compensation source 38. The voltage tap ofpotentiometer 90 is joined to common input lead 74 of summer circuit 28through. a series resistor R 11. Adjustmerrt of the potentiometer tapbetween the positive and negative voltage limits provides residual flowcompensation for power transfer in either direction 'in transmissionline 12.

The combined power, rate, and compensation signals at common lead 74 arefed to an amplifier 92 in the summer circuit 28. A resistor R and acapacitor C are each connected in parallel across the input and outputterminals of amplifier 92. Resistor R and capacitor C provide a filtertime constant determinative of the summation value for relay pickup. Thetime constant at which relay pickup would be produced for a step signalmay be adjusted by the relative size of capacitor C while maintainingthe value of R constant.

The output of summer circuit 28 is fed to an ammeter 94 through areversing switch 96. As current flow may be either in the positive ornegative direction in the circuit, depending upon the direction and rateof change of power transfer in line 12, the reversing switch is providedto enable use of a directional meter. Since optimum adjustments of therelay are expected to compromise between operating conditions and sincesetting procedures will differ from those for more conventional relays,the relay 10 is designed to provide a continuous indication of itsoutput signal as a per unit of trip setting. The ammeter 94 is aconventional meter calibrated from zero to 1.0. The tripping pointcorresponds with the full scale reading of 1.0. The full scale readingis adjustable for the range of power, rate, and compensation values bymeans of a shunting potentiometer 98 in parallel with a resistor R Understeady state power transfer conditions the meter indication isproportional to power flow on line 12. When the power transfer isincreasing, the reading is higher than the steady state reading by therate of increase.- Conversely, when the flow is decreasing, theindication is less than that for steady state conditions by the rate ofdecrease.

The output of ammeter 94 is fed to the center tap of a biasing coil 100.Sensitive operating relay X and X are each joined to an end of coil 100.The other ends of relays X and X are joined to ground through blockingnetwork 44. Opposed Zener diodes Z and Z, are joined in parallel withcoil 100 and relays X and X represented in'FlG. 2 as relay coils, toprotect the relay coils from overloads. Coil 100 is magnetically coupledto a coil 102 through'a common core 104. Coil 102 is joined at one endin series with a resistor R and the low voltage AC output 64 of powersupply 60, and at the other end is joined to ground. Low voltage ACinduced in coil 100 is effective to neutralize residual magnetism in thecoils of relays X and X When blocking network 44 is open, the output ofamplifier 92 will pass to ground through the coils of relays X and X,.Relay X energizes a system monitoring recorder (not shown) when theinput voltage from summer'circuit 28 reaches a predetermined percentageof the trip setting of relay X Common leads 106 and 108 are connected tothe low voltage AC output terminals 68 and 70 of stepdown transformer66. A relay contact X of relay X and the coil of a relay X outputterminals 114 and 116. The output circuit 50 energized by contacts X iselectrically isolated from the remainder of relay 10 and activates ahigh voltage circuit breaker (not shown) to interrupt power flow intransmission line 12.

Relay X; is sensitive to the output magnitude of summer circuit 28 andtrips for both positive and negative signals. When the output of thesummer decreases below the relay trip setting, contacts X open,deenergizing relay coil X, and opening contacts X Relay X remainsclosed, however, since a seal in current is shunted from relay contactX;," to relay coil X across conductor 112. Relay X5, must be reset toclear the main trip contact X and the lamp 110.

A blocking network 44 for preventing activation of relay 10 by spuriousrate signals is shown in FIG. 3. Input to the blocking network from thesummer circuit 28 is provided at terminal 118 of the blocking network.Input of the rate signal from the differentiator 30 is provided to theblocking network at input terminal 120. Positive and negative biasingvoltages are provided from power supply 60 at terminals .56 and 58 ofthe blocking network.

Positive signals from summer 28 pass to ground through the blockingnetwork via terminal 118 in series with a diode D and an NPN transistorT The anode of diode D is connected to terminal 118 and the cathode tothe collector of transistor T The emitter of transistor T is connectedto ground. The base of transistor T is connected to positive terminal 56through a diode D and a biasing resistor R providing a positive biaswhich holds the transistor conductive as long as rate signals in thenormal operating range of relay 10 are received at input terminal 120.Since the operation of relay 10 is bidirectional, parallel provision ismade for negative signals from summer 28. This parallel provisionincludes a diode D in series with a PNP transistor T connected betweenterminal 118 and ground. A diode D and a resistor R cooperate tonegatively bias transistor T in a conductive mode for negative powerflow when normal rate signals are received at terminal 120.

The rate signal from differentiator circuit 30 is fed to the blockingnetwork at input terminal 120. The base of an NPN transistor T isconnected to terminal 120 through an input reare connected in seriesbetween common leads 106 and 108.

The relay contact X of relay X and a relay coil of a 'multicontact relayX are similarly connected in series between common leads 106 and 108.The low voltage contact X;, of relay X and a target lamp 110' are alsoconnected in series between terminals 106 and 108. A lead 112 isconnected between relay contact X and X;, on the side of the contactsremoved from common lead 106,

When the output of summer circuit 28 reaches the trip setting of relay Xthe relay is activated, closing contacts X, which energize relay coil XActivation ofrelay X closes contacts X which energize relay coil Xclosing contacts X and X while simultaneously energizing target lamp 110to indicate that the relay circuit has been tripped. High voltagecontacts X of relay X close the circuit 50 between relay 10 sistor RResistors R 9 and R are connected in series between positive terminal 56and the base of transistor T A resistor R is connected between the baseof transistor T and negative terminal 58. The collector of transistor Tis connected between resistors R and R and the emitter is connected toground. The relative values of resistors R R and R are chosen with theresistance of R much larger than the sum of the resistances of R and RResistor R serves as a biasing resistor for transistor T biasing thetransistor into the conductive mode.

The base of a PNP transistor T is connected to the collector oftransistor T Resistor R which is also connected to the collector oftransistor T serves as a biasing resistor to establish the operatingpoint of transistor T The emitter and collector of transistor T areconnected to the positive and negative terminals 56 and 58 of powersupply 60, respectively, through equal value resistors R and R,;,.

A positive rate signal received at terminal of the blocking networkcauses transistor T to become more conductive, increasing the negativebias on transistor T As the negative bias increases to and beyond theabnormal range, transistor T becomes more conductive and the emitter ofthe transistor becomes more negative, while the collector becomes morepositive. The gate of a silicon controlled rectifier SCR, is connectedto the collector of transistor T through series resistors R and acapacitor C The gate of SCR is also connected to the negative terminal58 through a biasing resistor R As the collector of transistor T swingsto the positive a transient current, conducted through resistor R andcapacitor C fires SCR The anode of SCR is connected to positive terminal56 through a series resistor R and the cathode is connected to negativeterminal 58. A capacitor C in series with a resistor R is shuntedbetween terminal 58 and the anode of SCR,. A

resistor R is connected between the gate of SCR and terminal 58, puttinga negative bias on the SCR gate .to prevent gating by noise pulses, andto provide gating pulse limiting to protect the SCR.

When a gating pulse fires SCR,, capacitor C discharges rapidly throughresistor R and SCR,. The base of NPN transistor T, is simultaneouslydriven to the negative, causing the transistor to stop conducting, andpreventing activation of the tripping relay. Capacitor C then rechargesaccording to a time constant determined by the values of R and RCapacitor C then blocks tripping for' steady state conduction throughtransistor T as T again becomes conductive.

Similar provision is made for turning off transistor T; when a negativerate signal is received at input 120. A negative rate input drives theemitter of transistor Trmore positive causing a gating pulse to flowthrough a capacitor C in series with a resistor R to the gate of asilicon controlled rectifier SCR Resistor R serves a function analogousto that of resistor R while resistor R and capacitor C are analogous toR and C respectively. Thus, when an abnormal negative rate pulse isreceived at terminal 120, indicating that the rate of power flow isdecreasing, the relay is deactivated for power flow in the negativedirection. Since positive rates of change associated with negative powerflow, and negative rates of change associated with positive power flowhave neutralizing effects when the power and rate signals are added atthe summer circuit, the blocking network is not responsive to thesecombinations of signals. The values of the circuit elements in theblocking network are chosen to prevent blocking for rate signals in therange harmful to transmission line 12,

while blocking those rate signals which are of a spurious nature.

in one exemplary form of the invention the circuit parameters were asfollows: Amplifiers 54,76, and 78 were P65AU Philbrick operationalamplifiers, while amplifier 92 was a P45AU Philbrick operationalamplifier. D and D, were [N646 diodes, while D3--D5 were lN464 diodes. Zand Z were lN3060B Zener diodes. T and T were 2N708 transistors, while Tand T were 2N2 l 87 transistors. SCR, and SCR, were 2N2322A siliconcontrolled rectifiers. Relays X and X were 2MA DC 2500 ohm, SPST Sigma48RO 2500G-STL relays. Relays X and X were 6.3 volt AC DPDT Alliedcontrol B06-A relays. The power supply 60 was a PR30C Philbrickregulated power supply providing positive volt'DC output at terminal 56and negative 15 volt DC output at terminal 58, with a 6.3 volt AC outputat terminal 64 for a 1 15 volt AC in- 7 power transfer environment,numerous modifications of the put. The stepdown transformer 66 provided6.3 volt AC out- I put at terminals 68 and 70 for a 1 l5-volt AC input.-A Hall watt transducer delivering an output of 0 to 100 millivolts DCwas used as the input to the relay 10. The values of the resistors usedin the circuit were, in ohms: R 5.1K; R,, R,,,, R R 4.7l(; R, 390K; RR,, R,,,- 10K; R 160K; R R R R R 120K; R R 25K; R 250K; R 100K; R 28; R2.5K; R 10K; R 3OK;YR 1.5K; R --5.6K; R R 18K; R R 33K. Potentiometers72 and 88 were 5K ohms, potentiometers 8t) and 82 were 10K ohms, andpotentiometer 98 was 0.5K ohms. The values of capacitors uses were, inmicrofarads: C. 5; C, 0.33; C. 10;C, 6; C 1.2; C 1.3; C,,,; C 20.

It can thus be seen that a useful device for monitoring the powertransfer characteristics of an electrical transmission network has beenprovided.

in adapting the present exemplary disclosure to a particular inventionwill become apparent to those skilled in the art in the light of theabove teachings and within the scope of the appended claims.

It is claimed: 1

1. Apparatus for monitoring and controlling power transfer in anelectrical circuit comprising;

means for measuring the amount of power transfer in the electricalcircuit and providing a first output signal representative of thatamount; means for measuring the rate of change of power transfer in theelectrical circuit and providing a second output signal representativeof that rate of change;

means for combining the first and second output signals to provide acombined signal; and

means selectively responsive to the combined signal for providing acontrol signal for controlling the power transfer in the electricalcircuit.

2. An apparatus as described in claim 1, further comprising:

means for providing a third output signal representative of residualpower transfer in the electrical circuit; and

the means for combining further including means for incorporating thethird output signal into the combined signal.

3. An apparatus as described in claim 1 in which:

the means for measuring the amount of power transfer includes a powertransducer;

the means for measuring the rate of change of power transfer includes adifferentiator circuit with an input from the power transducer; and

the means selectively responsive to the combined signal includes a triprelay which activates a control circuit.

4. An apparatus as described in claim 2 in which:

the means for measuring the amount of power transfer includes a powertransducer;

the means for measuring the rate of change of power transfer includes adifferentiator circuit with an input from the power transducer; and I vthe means selectively responsive to the combined signal includes a triprelay which activates a control circuit.

5. An apparatus as described in claim 1, further comprising:

means for limiting the magnitude of the second output signal; and

means for blocking the control signal when the magnitude of the rate ofchange of power transfer in the electrical circuit exceeds a designlimit.

6. An apparatus as described in claim 2, further comprising:

means for limiting the magnitude of the second output signal; and

means for blocking the control signal when the magnitude of the rate ofchange of power transfer in the electrical circuit exceeds a designlimit.

7. An apparatus as described in claim 3, further comprising:

means for limiting the magnitude of the second output signal; and

means for blocking the control signal when the magnitude of the rate ofchange of power transfer in the electrical circuit exceeds a designlimit.

8. An apparatus as described in claim 4, further comprising:

means for limiting the magnitude of the second output signal; and

means for blocking the control signal when the magnitude of the rate ofchange of power transfer in the electrical circuit exceeds a designlimit.

1. Apparatus for monitoring and controlling power transfer in anelectrical circuit comprising: means for measuring the amount of powertransfer in the electrical circuit and providing a first output signalrepresentative of that amount; means for measuring the rate of change ofpower transfer in the electrical circuit and providing a second outputsignal representative of that rate of change; means for combining thefirst and second output signals to provide a combined signal; and meansselectively responsive to the combined signal for providing a controlsignal for controlling the power transfer in the electrical circuit. 2.An apparatus as described in claim 1, further comprising: means forproviding a third output signal representative of residual powertransfer in the electrical circuit; and the means for combining furtherincluding means for incorporating the third output signal into thecombined signal.
 3. An apparatus as described in claim 1 in which: themeans for measuring the amount of power transfer includes a powertransducer; the means for measuring the rate of change of power transferincludes a differentiator circuit with an input from the powertransducer; and the means selectively responsive to the combined signalincludes a trip relay which activates a control circuit.
 4. An apparatusas described in claim 2 in which: the means for measuring the amount ofpower transfer includes a power transducer; the means for measuring therate of change of power transfer includes a differentiator circuit withan input from the power transducer; and the means selectively responsiveto the combined signal includes a trip relay which activates a controlcircuit.
 5. An apparatus as described in claim 1, further comprising:means for limiting the magnitude of the second output signal; and meansfor blocking the control signal when the magnitude of the rate of changeof power transfer in the electrical circuit exceeds a design limit. 6.An apparatus as described in claim 2, further comprising: means forlimiting the magnitude of the second output signal; and means forblocking the control signal when the magnitude of the rate of change ofpower transfer in the electrical circuit exceeds a design limit.
 7. Anapparatus as described in claim 3, further comprising: means forlimiting the magnitude of the second output signal; and means forblocking the control signal when the magnitude of the rate of change ofpower transfer in the electrical circuit exceeds a design limit.
 8. Anapparatus as described in claim 4, further comprising: means forlimiting the magnitude of the second output signal; and means forblocking the control signal when the magnitude of the rate of change ofpower transfer in the electrical circuit exceeds a design limit.